The Wheel Geometry: 6 Critical Focus Points

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1. What is the Castor angle?

Castor is a term used in the automotive industry to describe the angle of a steering axis relative to a vertical line when viewed from the side of a vehicle. It is measured in degrees and is an important aspect of wheel geometry as it affects the handling and stability of a vehicle. Castor is the angle between the steering axis and the vertical line and is often referred to as the “kingpin” angle. A positive castor angle provides stability, but negative castor reduces stability. The ideal castor angle varies depending on the type of vehicle, driving conditions, and driver preference. It is crucial to get the castor angle correct for safe and efficient handling of a vehicle.

positive castor
1. Positve Castor

2. What is Camber?

Camber refers to the angle at which the wheels of a vehicle are inclined, either toward the center or away from it, when viewed from the front or rear. It is an important aspect of wheel geometry as it affects the handling and stability of a vehicle. Positive camber means the wheels are angled outward from the center, while negative camber means the wheels are angled inward.

"Diagram showing positive and negative camber angles on a car wheel, with an incline illustration representing the tilt of the tire towards or away from the centerline of the vehicle"
1. Negative & 3.Positive camber

A correct camber angle is essential for proper tire wear, handling, and stability. It helps distribute weight evenly across the tires and maintains traction during turns. The ideal camber angle depends on the type of vehicle and its intended use. For example, racing vehicles typically have a lot of negative camber for improved handling, but this could cause excessive tire wear on a daily driver. Camber can be adjusted through suspension components and is an important aspect of vehicle alignment.

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Steering axis inclination

3. What is Steering Axis Inclination

Steering Axis Inclination (SAI) is an angle that represents the tilt of a steering axis as viewed from the front of a vehicle. The steering axis is an imaginary line that runs through the center of the steering knuckle and the ball joint. SAI is used to measure the camber angle of the wheels relative to the vertical axis of the vehicle. It is an important aspect of wheel geometry as it affects the handling and stability of a vehicle.

A positive SAI means that the steering axis tilts away from the vertical axis, while a negative SAI means it tilts towards it. A correct SAI angle helps to reduce tire wear and improve stability by reducing the scrub radius. The scrub radius is the distance between the centerline of the tire and the steering axis. A large scrub radius can cause poor handling and increased tire wear. The ideal SAI angle varies depending on the type of vehicle, driving conditions, and driver preference. It is crucial to get the SAI angle correct for safe and efficient handling of a vehicle.

4. What is Included Angle?

The Included Angle is the angle between the steering axis and the centerline of the wheel, which affects the handling and stability of a vehicle. It is important to have a correct included angle to ensure safe driving and prevent excessive tire wear.

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5. Thrust Angle

thrust angle refers to the angle between the centerline of a vehicle and the direction it is driving in. It is caused by unequal tire pressure, misaligned suspension components, or uneven wear on the tires. A correct thrust angle is essential for proper handling and stability as well as even tire wear. An incorrect thrust angle can cause the vehicle to pull to one side, reducing driving comfort and safety. Regular alignment checks and tire maintenance can help prevent a misaligned thrust angle.

6. Toe-in & Toe-out

Toe in and Toe out refer to the angle at which the wheels are pointing relative to the centerline of the vehicle. Toe in means that the front of the wheels are closer together than the rear, while Toe out means the front of the wheels are further apart. The toe is an important aspect of wheel geometry as it affects the handling and stability of a vehicle, as well as tire wear. An incorrect toe angle can cause uneven tire wear and reduce handling stability. Regular alignment checks and tire maintenance can help prevent a misaligned toe angle.

"Toe-in and Toe-out depicted on a car wheel, with arrows pointing towards the direction of the tire rotation relative to the centerline of the vehicle"
Toe-in & Toe-out

Conclusion

wheel geometry plays a crucial role in the handling and stability of a vehicle. Understanding concepts such as castor, camber, steering axis inclination, included angle, thrust angle, toe in, and toe out is essential for ensuring safe and efficient driving. Regular alignment checks and tire maintenance are important in maintaining a correct wheel geometry and preventing any issues. A properly aligned wheel geometry can improve driving comfort, increase fuel efficiency, and extend the lifespan of tires.

Also see: Electronic Brake Distribution System: Improving Vehicle Safety with Enhanced Control and Precision. – TheAutoEngineer.com

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